The conventional internal-combustion engine, used heretofore almost exclusively in automotive vehicles, is one of the major contributors to the pollution of the environment, especially in urban centers of high traffic density. This is due to the fact that the extremely brief ignition period does not allow complete combustion of the air/fuel mixture so that the exhaust gases are rich in toxic constituents such as carbon monoxide. Another drawback of such engines is the noise due to their intermittent mode of operation, particularly in the case of motors running close to their rated capacity. This problem is aggravated by the current tendency to lower fuel consumption through reduction of the power ratings of automotive engines.